Summary

The efficiency of pulsed UV light (PL) for inactivation of E. coli K12 on hard-cooked eggs was investigated. Temperature, colour and texture were recorded to determine adverse effects on quality. Distance from the quartz window (5.5, 9.5 cm) and time (1–30 s) was set as the experimental variables. Results indicated that E. coli K12 viability decreased at closer distances and increased time (P < 0.05). Bacterial populations were reduced to 3.54 log CFU per egg and 3.23 log CFU per egg after 15 and 20 s at 5.5 cm and 9.5 cm, respectively. Scanning electron micrographs revealed the existence of photophysical mechanisms, bacterial overlapping and internalisation interfering inactivation. Treated samples experienced slight thermal increases (6–9 °C) contributing to the preservation of colour and texture, not significantly different from untreated samples (P > 0.05). Our findings support the use of PL to enhance the safety of hard-cooked eggs although bacterial shadowing may have significant implications on treatment efficiency.